The subject of the invention is a method of assembling the electrodes of an electron gun for a cathode-ray tube and, more particularly, electrode shapes which allow the implementation of the process. The invention is particularly adapted to electron guns for cathode-ray tubes with improved resolution.
An electron gun takes the form of a succession of electrodes drilled with one or more openings for the passage of the electron beans intended to form an image on the screen of the tube in which the gun is inserted. On their peripheral surface, these electrodes generally possess metal claws which will be inserted, hot, into glass beads intended to keep the stack of electrodes constituting the gun in place. The openings located on two facing electrodes constitute electron lenses intended to act on the trajectory or the shape of the electron beams passing through them. The relative positioning of the openings of the electrodes is therefore extremely critical and must be performed with great accuracy. The openings of the various electrodes have long been circular and concentric, so that the gun needed to be assembled by stacking the electrodes one above another, cylindrical rods passing through the openings automatically positioning these openings with respect to one another.
Present-day electron guns are required to provide even finer supervision of the trajectory and the shape of the electron beams, this leading to the design of ever more complex electrostatic lenses. This complexity is manifested by the fact that the openings of the electrodes often have shapes which are far removed from the previous circular shapes, and that the openings of two successive electrodes are no longer coaxial as in the past. As a result, the methods of assembly of the prior art and in particular the methods of relative positioning of the openings by virtue of rods passing through them are no longer applicable.
The invention is a method of assembly which is a convenient and efficient. The method does not utilize the openings of the electrode themselves as the reference positions, but rather relies on the shape of the periphery of the electrodes for alignment.
Accordingly, the method of assembling an electron gun for a cathode-ray tube according to the invention is characterized in that it comprises the following steps:
loading of at least two electrodes one above the other;
adjusting the distance between the electrodes along the longitudinal axis of the gun, for example, by use of wedges of given thickness arranged between the electrodes;
loading the electrodes between the two jaws of a positioning tool;
relatively positioning of the electrodes in the plane perpendicular to the longitudinal axis by clamping the jaws of the tool in a single direction, until a pressure is exerted on the four corners of each electrode;
final retentioning by hot insertion of glass beads into claws arranged on the periphery of the electrode openings of the positioning tool.
The tool for positioning electron gun electrodes for implementing the invention is characterized in that, in the plane perpendicular to the longitudinal axis of the gun, the jaws have a profile intended to cooperate with the shape of the corners of the electrodes in such a way that upon closure of the jaws, the electrodes are brought to their nominal position in the plane perpendicular to the longitudinal axis.